A display device in which a touch panel, for which an input operation can be performed by touching it using a finger or the like, is mounted, by being built in a system controlling a display content and the operation of a device in accordance with an input operation, contributes to the realization of interactive operability enabling easy use. For this reason, information apparatuses such as a smartphone having a touch panel built therein, a tablet terminal, and a notebook personal computer have rapidly been spread widely.
Meanwhile, the surface of a display device having a touch panel mounted thereon is evenly hard, and a same tactile sense is acquired when any portion displayed on the screen is touched. For this reason, it is practically difficult to perceive portions of a touch panel for which an effective input can be made through a touch operation and whether or not an effective input is made without seeing the touch panel. Thus, it is difficult to operate such a device only depending on a tactile sense without seeing the screen of the display device.
In contrast to this, for example, a remote controller of a television receiver, a conventional mobile phone terminal (feature phone), a keyboard of a personal computer, and the like respectively include independent operation keys, and accordingly, the position of an operation key can be perceived depending on only a tactile sense, and, also when such an operation key is pressed, it can be perceived through a tactile sense. Thus, in a case where the positions and the arrangement of operation keys are memorized, it is not that difficult to operate the operation keys depending on only a tactile sense.
From such backgrounds, technologies for applying a tactile sense to a display device have been researched. Such technologies, for example, include a method of mechanically vibrating a display device using a piezoelectric device, an eccentric motor, or the like; a method of presenting a tactile sense (texture sense) when a device is traced using a finger by changing a frictional force between an operator's finger and a device using an electrostatic force, a so-called method using an electric vibration phenomenon; and a method of driving a nerve axon of a cutaneous mechanoreceptor of a user's finger by causing an electric current to flow through the finger.
Among such methods, relating to the method using the electric vibration phenomenon, for example, in Japanese Patent OPI Publication No. 2011-248884, a tactile sense presentation device has been proposed which includes a conductive face; an insulating face arranged on the conductive face and a controller configured such that a signal is coupled with a user being in contact with the device and thus, causing at least one finger of the user sliding on the insulating face to perceive a tactile sense.
A tactile sense presentation device using the electric vibration phenomenon includes an electrode and an insulating layer protecting the electrode and presents a tactile sense to an operator through the following mechanism when an operator's finger moves on the insulating layer.
(1) When a voltage signal is applied to the electrode, an electrostatic force is applied between the electrode and the operator's finger. The electrostatic force is constantly an attractive force, and the electrostatic force changes according to the frequency of the voltage signal.
(2) As a normal reaction applied between the operator's finger and the surface of the insulating layer changes according to a change in the electrostatic force, when the user slips his finger on the surface of the insulating layer, the frictional force changes according to the frequency of the voltage signal.
(3) The change in the frictional force changes a force applied in the shearing direction of the finger, and deformation of the finger according to the frequency of the voltage signal is caused. Such a deformation (mechanical vibration) is detected by a mechanoreceptor of the user's finger, and accordingly, a rough texture sense is perceived.
In order to allow a rough texture sense to be perceived as above, it is necessary to apply an appropriate voltage to the electrode such that an appropriate electrostatic force is applied between the electrode and the operator's finger. However, it is not easy to apply an appropriate voltage, and, when the voltage applied to the electrode is increased so as to allow a texture sense to be easily perceived, in a case where an insulating film protecting the electrode disappears due to abrasion or the like, a high voltage is applied to the operator's finger, and there is concern that an inappropriate current flows through the operator's finger, and it is not desirable from the viewpoint of safety. On the other hand, when the voltage applied to the electrode is decreased, a sufficient texture sense cannot be perceived.
Particularly, a contact face (the surface of the insulating layer) of a conventional tactile sense presentation device is flat, and, in case of the flat contact face, the finger is tightly brought into contact with the contact face and is difficult to slide, whereby it is difficult to perceive a texture sense. For this reason, it is necessary to further increase the voltage applied to the electrode, and it is difficult to secure the safety. Accordingly, there is a problem in that it is difficult to achieve both easy perception of a texture sense and a decrease in the voltage applied to the electrode.
The present invention is made in consideration of the problems described above, and a main object thereof is to provide a tactile sense presentation device capable of allowing a texture sense to be easily perceived and effectively decreasing the voltage applied to the electrode, an electronic apparatus including the tactile sense presentation device, and a method of driving a tactile sense presentation device.